The present invention relates to a display lamp capable of performing digital display of a numerical value as well as a mark, letter or symbol, and more particularly to an improvement suited for use in a display panel for aircraft due to its excellent brightness and distinction in the digit, mark, letter or symbol displayed.
For the reason that a display unit S of such a lamp is required to be able to display any of digits from 0 to 9, it is constituted by a total of several display elements which consist of at least three parallel horizontal elements and at least four vertical elements coupling the ends of the horizontal elements in a manner to shape a character " " and are switched on or off selectively to display a desired digit. In general, each display element can be composed of a liquid crystal, light emitting diode or filament. In a display panel for aircraft, however, a filament is employed to meet the requisites of high display brightness and distinction.
In a display unit S using filaments, it is necessary to attain clear display in the corner connections where the seven display elements intersect one another and, in case satisfactory clearness is not attained, the digit or mark, letter or symbol displayed becomes indistinct to render reading difficult.
For the purpose of ensuring the required clearness, there is proposed an exemplary device as illustrated in FIG. 1 where vertical and horizontal display elements are so disposed as to intersect each other at the corners. However, if the display elements employed are filaments, electrical conduction occurs among them as a result of mutual intersection and contact of the filaments, thereby making it impossible to switch on the desired filaments alone selectively. And thus, it becomes necessary to prevent mutual contact between the horizontal and vertical filaments at the corners by spatially separating them from one another for isolation.
In a known display lamp shown in FIG. 1, filaments A, G and D for horizontal lines and filaments B, C, E and F for vertical lines are arrayed on different spatial planes to be kept out of mutual contact. And the ends of the individual filaments are positioned on electrodes 1 through 12 respectively, of which 2, 3, 4, 5 and 9 serve as common electrodes enabling mutual conduction. Supposing that the electrodes 2, 4, 5, 8 and 11 hold the high-level horizontal filaments A, G and D, then the remaining electrodes 1, 3, 6, 7, 9 and 12 are to hold the low-level vertical filaments B, C, E and F. It is necessary, therefore, that internal leadwires 22, 24, 25, 28 and 31 are slightly longer than internal leadwires 21, 23, 26, 27, 29 and 32, and the electrodes 2, 4, 5, 8 and 11 are positioned on a high-level plane in the display unit S while the other electrodes 1, 3, 6, 7, 9 and 12 are positioned on a low-level plane. It is also necessary to maintain filaments B, C, E and F out of contact with internal leadwires 21, 23, 26, 27 and 29. The position of the filaments is determined according to the sealing position of the leadwires and the display quality of the display lamp is affected thereby. It is therefore necessary that the position of the leadwires in the stem or the display unit be precisely determined.
In addition to the above, eight leadwires 41 through 48 are required for external lead terminals. In the prior art, two groups of such external leadwires, each consisting of four leadwires, protrude in parallel with one another as illustrated in FIG. 2 to form terminals b, a, g, c and f, h, d, c, with the terminal h serving as the aforementioned common electrode.
In a socket 16 shown in FIG. 3, the internal leadwires 21 through 32 and the external leadwires 41 through 48 are connected as follows: external leadwire 46 having common terminal h is connected to internal leadwires 22, 23, 24, 25 and 29 having electrodes 2, 3, 4, 5 and 9; external leadwire 42 having terminal a is connected to internal leadwire 31 having electrode 11; external leadwire 41 having terminal b is connected to internal leadwire 21 having electrode 1; external leadwire 44 having terminal c is connected to internal leadwire 26 having electrode 6; external leadwire 47 having terminal d is connected to internal leadwire 28 having electrode 8; external leadwire 48 having terminal e is connected to internal leadwire 27 having electrode 7; external leadwire 45 having terminal f is connected to internal leadwire 32 having electrode 12; and external leadwire 43 having terminal g is connected to internal leadwire 30 having electrode 10.
In the display unit S, hermetic sealing glass is poured onto the bottom of its metallic side wall drawn downward slightly, and the internal leadwires 21 through 32 are sealed therein with the glass to constitute a stem. The filaments are set directly on leadwires 21-32, adjacent to each other with the spaces between the leadwires being narrow. However, despite the narrow spaces it is necessary for the internal leadwires to be spaced in the glass without disturbing their positioning. In the socket 16, the external leadwires 41 through 48 are fixed firmly, and a face glass member is provided hermetically on the top of the metallic side wall.
Therefore, in manufacture of a conventional display lamp, first a high-precision stem is composed of upper-level and lower-level internal leadwires 21 through 32 for setting the filaments A through G individually, and then the stem thus obtained is connected to the external leadwires 41 through 48 in the socket. Consequently, there exist some disadvantages including that a large number of components are required and the number of manufacturing processes becomes extremely great to bring about an increase of production cost.